Postβ-Lactamase-Inhibiting Effect of Sulbactam in Combination with Ceftriaxone on Extended-Spectrum-β-Lactamase-Producing Escherichia coli

Background/Objectives: Extended-spectrum β-lactamase (ESBL)-producingEscherichia coliposes a significant global health challenge, as it leads to antimicrobial treatment failure and is associated with elevated mortality rates. The use of β-lactam/β-lactamase inhibitor combinations offers an alternative approach for combating ESBL-producing bacteria. Ceftriaxone (CRO) and sulbactam have been coadministered in the clinical settings; however, discrepancies in their pharmacokinetics raise concerns regarding the rationality of this combination.Methods: This study was designed to investigate the postβ-lactamase inhibitor effect (PLIE) under both static and dynamic conditions, with the aim of supporting the clinical application of this combination.Results: The minimum inhibitory concentration (MIC) of CRO/SBT (2:1 ratio) againstE. coliNCTC 13353 was determined to be 32/16 μg/mL. The PLIEs were determined to be −1.26, −0.57, and 0.37 h at CRO/SBT concentrations ranging from 1/2 MIC to 2 MIC, respectively. The results of CRO concentration, β-lactamase activity,blaCTX-M-15expression, and cell morphology collectively support that SBT exerts PLIEs and protects against the antibacterial activity of CRO. In the dynamic hollow-fiber infection model, CRO monotherapy showed no inhibitory effect onE. coli, whereas CRO/SBT combination therapy rapidly eliminated SBT, achieved comparable bactericidal effects, prolonged CRO exposure, and maintained low β-lactamase activity levels.Conclusions: In conclusion, CRO/SBT exerts an inhibitory effect on enzyme-producing strains by being able to produce PLIE to maintain the inhibition of β-lactamase.